The field of the disclosure relates generally to fiber communication networks, and more particularly, to access node transmission techniques for communication networks capable of transmitting coherent optical signals.
Fiber-based cable networks have been widely deployed in many regions of the world. Increasing demand for high-speed data and video services is presently driving growth in access bandwidth requirements for both residential offerings and for business subscribers. The amount of fiber resources available to such conventional networks, however, has remained fixed. A number of multiplexing approaches have been conventionally implemented to support the growing demand on the cable networks, using the available fiber resources. One presently popular approach uses wavelength division multiplexing (WDM). The RF cable spectrum is carried over a fiber by subcarrier multiplexing (SCM) the data and video channels over an optical carrier that (i) is intensity-modulated, (ii) uses a directly-modulated laser, or (iii) uses external modulation. The optical signals of these multiplexed optical carriers require a very high signal-to-noise ratio (SNR) to carry the high quality cable RF signals.
To achieve the required high dynamic range necessary for the high SNR, transmission lasers at the hub of the operator are required to operate at very high power levels, which is both difficult and expensive to implement in practice. A recent approach to achieve this high SNR requirement digitizes the RF signal and carries the digitized signal through the optical digital transport, as disclosed in co-pending U.S. application Ser. No. 15/847,417, filed on Dec. 19, 2017, the disclosure of which is incorporated by reference herein.
FIG. 1 is a schematic illustration of a conventional cable network 100 operable to provide video, voice, and data services to subscribers. Cable network 100 includes a hub 102, a node 104, and end users 106 (e.g., residential users 106(1), business users 106(2), cellular base stations 106(3), etc.). A long fiber 108 carries digital optical signals and or digitized RF signals between hub 102 and fiber node 104. In some embodiments, an electrical-to-optical (E/O) modulator 110 is disposed between hub 102 and long fiber 108. Respective end users 106 are disposed along a plurality of short fiber segments 112 (four short fiber segments 112 illustrated in FIG. 1), which are divided at node 104 by a plurality of sub-nodes 114. Such sub-node splitting techniques are running out of capacity to meet the growing demand for bandwidth over existing long fibers 108. Accordingly, improved techniques are needed to effectively split a node into independent streams, in order to provide additional capacity to a segment of the node without significantly increasing an outlay of fiber resources.